pediatric anesthesia: a review - glowm...peripheral nerve blocks 2.1 upper extremity blocks...

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Ultrasound Imaging for Pediatric Anesthesia: A Review

Santhanam Suresh MD, Lauren J. Taylor BA and Amar S. Minhas Department of Pediatric Anesthesiology, Children’s Memorial Hospital,

Northwestern University Feinberg School of Medicine, Chicago, IL

USA

1. Introduction

There has been a recent increase in the use of regional anesthesia in pediatric patients

(Lacroix, 2008). This explosive growth, particularly in the use of truncal blocks, can be

attributed in part to the refinement of anatomically based ultrasound imaging to facilitate

nerve localization. Historically, pediatric regional anesthesia has posed a significant

challenge due to the close proximity of nerves to critical structures and the need for limiting

the local anesthetic volume below toxic levels in children. Ultrasound guidance, however,

allows the visualization of important anatomy and can help overcome many of these

traditional obstacles.

This chapter will review a variety of common peripheral nerve and central neuraxial blocks

that can be performed using ultrasound guidance in children. This aspect of regional

anesthesia has the potential for significant contributions to evidence-based medicine.

Because ultrasound guidance is a relative newcomer to the field of regional anesthesia, most

of the current literature is not evidence based. As a result, much of the data comes from case

reports and case series. This chapter is based on an extensive review of the literature using

MEDLINE and EMBASE from 1980 to May 28, 2009. Our goal is to provide the pediatric

anesthesiologist with a comprehensive summary of the relevant sonoanatomy, techniques,

and outcomes of ultrasound guidance for peripheral nerve blocks of the extremities and

trunk as well as neuraxial blocks in pediatric patients based on currently available literature.

2. Peripheral nerve blocks

2.1 Upper extremity blocks Peripheral regional anesthesia is of great utility in children undergoing surgery on the upper

extremities. Although many approaches to the brachial plexus have been described, the

axillary block using conventional methods is still the most commonly performed and reported

brachial plexus blockade in children. This may be due to the fact that other block sites are

situated near critical structures such as the cervical pleura (supraclavicular and infraclavicular)

and the spinal cord (interscalene). Although there is a paucity of related literature, the

introduction of ultrasound imaging will likely greatly increase the performance of brachial

plexus blocks in infants and children at locations besides the commonly described axillary

approach by allowing for real-time visualization of anatomical structures.

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2.1.1 Axillary block

2.1.1.1 Sonoanatomy

The axillary approach blocks the radial, median and ulnar nerves. A probe placed

perpendicular to the anterior axillary fold provides a short-axis view of the neurovascular

bundle with the biceps brachii and coracobrachialis muscles lateral and the triceps brachii

medial and deep to the biceps. The axillary artery is a useful ultrasound landmark and

appears as a circular anechoic structure adjacent to the biceps and coracobrachialis muscles.

Terminal nerves surround the artery with the radial nerve located deep and along the

midline of the artery. The median and ulnar nerves are both superficial to the artery, with

median nerve visible between the artery and biceps muscle while the ulnar nerve is found

more medial (Figure 1). It is important to be aware of anatomic variation, particularly in the

location of the median nerve. The musculocutaneous nerve is located between the

coracobrachialis and biceps muscles, but it is difficult to detect in children (Rapp & Grau,

2004). In contrast to the textbook anatomical description, in an ultrasound image the radial,

median, and ulnar nerves often appear the same size as the axillary artery (Rapp & Grau,

2004).

Fig. 1. Sonoanatomy of the axillary block location using a linear hockey stick probe (SLA 6-

13 MHz, 25-mm footprint) placed transversely to the humerus.

2.1.1.2 Technique

An axillary block may be used for procedures on the elbow, forearm, or hand. The use of

ultrasound guidance for this block in children, however, is not well described in the

literature; a recent search produced no original reports (Fleischmann et al., 2003). This block

may be performed in children using techniques borrowed from adult patients. With a

hockey stick or linear small footprint probe placed proximally in the axilla and transverse to

the humerus, an in-plane technique may be used. It is best to use multiple injections with

needle redirections to ensure that the local anesthetic surrounds all the terminal nerves of

the plexus. Due to the close proximity of the axillary vein and artery, multiple punctures

may be necessary to avoid intravascular injection.

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2.1.1.3 Outcome and discussion

In children, the axillary block is one of the most popular approaches to the brachial plexus

(Cregg et al., 1996). Due to the abundance of vessels in the axillary region, caution must be

taken when performing this block to avoid intravascular injection. This is particularly

important when multiple punctures are required to achieve the desired circumferential local

anesthetic spread. The use of ultrasound for real-time visualization may reduce this risk.

Color Doppler is also a helpful tool to identify the axillary vasculature. Due to the

superficial location of the plexus, ultrasound guidance may help the anesthesiologist guide

the needle advancement (Tsui & Suresh, 2010a).

2.1.2 Interscalene block

2.1.2.1 Sonoanatomy

Ultrasound imaging allows visualization of the C5, C6, and C7 nerve roots between the

anterior and middle scalene muscles (Figure 2). In a transverse oblique plane at the level of

the cricoid cartilage and at the posteriolateral aspect of the sternocleidomastoid muscle, the

muscle appears as a triangular shaped structure overlying the internal jugular vein and

common carotid artery. The scalene muscles serve as useful landmarks; the anterior scalene

lies deep to the sternocleidomastoid and lateral to the subclavian artery, while the middle

and posterior scalenes are located more posterolaterally. The neurovascular (interscalene)

sheath appears as a hyperechoic structure within the interscalene groove. The trunks and/ or

roots of the brachial plexus may be visible as round or oval-shaped hypoechoic structures.

Fig. 2. Sonoanatomy at the interscalene groove using a linear hockey stick probe (SLA, 6-13

MHz, 25-mm footprint).

2.1.2.2 Technique

For optimal imaging, the probe is placed in a transverse oblique plane at the level of the

cricoid cartilage. A combined ultrasound-guided nerve stimulating technique may facilitate

nerve localization. Using an in-plane approach and slight redirections to advance the needle

close to the brachial plexus, local anesthetic spread around the nerve roots or trunks may be

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visualized. Precise needle placement may limit the dose of local anesthetic required (Tsui &

Suresh, 2010a). This combined ultrasound guided-nerve stimulation technique has also been

described in the literature using an out-of plane approach and displacement of the middle

scalene muscle tissue as a means of tracking the needle tip (Fredrickson, 2007).


An interscalene approach is a means of providing analgesia for patients undergoing surgery

of the shoulder or proximal arm that can last 6-12 hours. This block may also be used for

catheter placement for continuous analgesia (Marhofer et al, 2005). While it may be

advantageous to use nerve stimulation in conjunction with ultrasound to confirm the

identity of the localized nerve root, a report documenting the performance of an interscalene

block in a 7-year-old child with femur fibula ulna syndrome suggests that ultrasound

guidance may be of special value for patients in whom the use of nerve stimulation is

impossible (Van Geffen et al., 2006).

Due to potential adverse effects including pneumothorax, vertebral artery injection, and

intrathecal injection, the intrascalene block is not common in pediatrics. Palpation of the

interscalene grove often proves challenging in children under general anesthesia and as a

result a recent report states that this block is not recommended for any heavily sedated or

anesthetized patient (Bernards et al., 2008). However, the improvements in nerve

localization made possible due to ultrasound guidance have the potential to increase the use

of this block in children.

2.1.3 Supraclavicular Block

2.1.3.1 Sonoanatomy

At the level of a supraclavicular approach, the trunks and divisions of the brachial plexus

are superiolateral to the subclavian artery and above the first rib. This relationship is most

clearly visualized with the probe in a coronal oblique plane. The subclavian artery may be

used as a primary ultrasound landmark and appears as an anechoic, hypodense, pulsatile

structure. Color Doppler may be useful to confirm vascular identification. The trunks and

divisions of the plexus appear as three hypoechoic grape-like clusters around the artery

while a hyperechoic line with dorsal shadowing indicates the first rib (Figure 3).

2.1.3.2 Technique

Literature describing the supraclavicular technique in children is limited (Suresh et al.,

2009). A recent report describes an approach similar to that used in adult patients (De Jose

Maria et al, 2008). With a high frequency probe in the coronal oblique plane, the plexus

divisions and/ or roots are visible lateral to the subclavian artery. Using an in-plane

approach, directing the needle from lateral to medial avoids vascular structures in contact

with the plexus. An out-of plane approach may also be successful.


The supraclavicular block may be performed for patients undergoing most procedures of

the upper extremities. However, when compared to other brachial plexus blocks there is an

increased risk of pneumothorax due to the proximity of the lung parenchyma at the level of

this block. By using an in-plane approach, ultrasound guidance may reduce this risk by

providing clear visibility of the needle shaft and tip, making the supraclavicular approach

one of the most reliable and effective blocks of the brachial plexus (Tsui & Suresh, 2010a).

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Fig. 3. Sonoanatomy at the supraclavicular block location using a linear hockey stick probe

(SLA, 6-13 MHz, 25-mm footprint) placed in the coronal oblique plane.

2.1.4 Infraclavicular block

2.1.4.1 Sonoanatomy

In the infraclavicular approach to the brachial plexus, the cords are located inferior and

medial to the coracoid process. Both the axillary artery and vein serve as useful ultrasound

landmarks for the infraclavicular approach. These vessels are located deep and medial to the

cords, with the vein positioned medial and caudal to the artery (Figure 4). Although all the

cords surround the artery, they are not visualized with equal clarity. The lateral cord is most

Fig. 4. Sonoanatomy at the infraclavicular block location using a linear hockey stick probe

(SLA, 6-13 MHz, 25-mm footprint) placed below the clavicle in a parasagittal plane.

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easily viewed and appears as a hyperechoic oval structure. In contrast, the posterior and

medial cords may be difficult to visualize, in part because the view may be obstructed by the

axillary vasculature; the medial cord lies between the artery and vein while the posterior

cord is deep to the artery. The pectoralis major and minor muscles lie superficial to the

neurovascular bundle and are separated by a hyperechoic lining (perimysium).

2.1.4.2 Technique

While the plexus lies quite deep in adults, the structure is much more superficial in children,

making a higher frequency probe optimal. Marhofer et al. described a lateral approach to

this block in which the probe was placed transversely below the clavicle with the patient in

the supine position (Marhofer et al, 2004). The authors achieved sufficient visualization of

the plexus in all 40 patients studied. With the needle inserted using an out-of-plane

approach 1 cm inferior to the probe, the local anesthetic dispersion was also clearly

visualized.

A recent report by De Jose Maria et al described a different technique in which the probe

was placed either parallel or in a slightly parasagittal plane to the clavicle (De Jose Maria et

al., 2008). The authors recommended using a medium frequency probe to maximize

visibility of deeper structures in older children. The needle was inserted cephalad to the

probe and redirected when necessary to ensure optimal spread of the local anesthetic

around the cords.


The infraclavicular block is commonly used for patients undergoing surgery of the upper

arm and elbow. It may also be a useful approach for placing a catheter in the posterior cord

during more extensive procedures. The risks of this block are similar to the supraclavicular

approach, with the danger of pneumothorax being most serious. Just as with the

supraclavicular block, an in-plane needle insertion under ultrasound guidance may

minimize the risk by allowing clear visualization of the needle tip and shaft (Chin et al.,

2008). In addition, due to the closer proximity of the cervical pleura to the plexus cords

medially, a lateral puncture site is recommended (Greher et al., 2002). Ultrasound imaging

may also be advantageous in avoiding multiple puncture sites and visualizing

underdeveloped structures like the coracoid process that may be difficult to palpate in

children using “blind” techniques (Marhofer et al., 2004; de Jose Maria & Tielens, 2004).

The first controlled study by Marhofer et al in 2004 compared ultrasound guidance to

traditional nerve stimulation technique for performance of the infraclavicular block in

children. The authors reported ultrasound guidance to be associated with superior visual

analog scores during block puncture, better sensory onset times (mean times of onset were 9

vs. 15 mins), longer duration of sensory block, and better sensory and motor block scores 10

mins after the block was performed. The authors explained the faster onset and longer

duration of the blocks by the more accurate deposition of local anesthetic possible under

ultrasound guidance (Marhofer et al, 2004). Although this study was a prospective,

randomized controlled blinded study, the authors did not comment on the power necessary

to determine statistical significance.

2.2 Lower extremity blocks Multiple regional anesthesia techniques may be used for children undergoing surgery of the

lower extremities, including lumbar plexus, femoral, and sciatic nerve blockades. These

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procedures can be performed successfully with the aid of ultrasound, which allows clearer

localization of structures as well as visual confirmation of the local anesthetic spread.

2.2.1 Lumbar plexus block

2.2.1.1 Sonoanatomy

Lumbar plexus blocks provide analgesia to the major branches of the lumbar plexus,

including the femoral, genitofemoral, lateral femoral cutaneous, and obturator nerves and

are therefore indicated for surgical procedures involving the hip, knee, or foot. In infants, a

transverse (axial) view using a linear probe reveals several bony structures including

spinous processes, laminae, and transverse processes, as well as musculature such as the

erector spinae and quadratus lumborum. The plexus is located deep to these structures and

is embedded in the psoas muscle (Figure 5). In a transverse scan, the spinous processes

appear hypoechoic (likely due to dorsal shadowing effect) and extend superficially, whereas

the transverse processes are hyperechoic masses or lines at the lateral edge of each vertebra.

In the longitudinal scan, the lateral edges of the transverse processes can be identified at the

most lateral point near multiple hyperechoic nodules (Tsui & Suresh, 2010a). In this view

the plexus lies between and just deep to the lateral tips of the processes.

Fig. 5. Sonoanatomy at the lumbar plexus block location using a linear probe (HFL38, 6-13

MHz, 38-mm footprint) placed transversely at L4/ 5.

2.2.1.2 Technique

With the patient in the lateral decubitus position, ultrasound guidance may be used to

identify the transverse processes of L4 or L5 and visualize the psoas major muscle and the

plexus in relation to the paravertebral musculature. To locate the bony landmarks, it is

important to alternate between transverse and longitudinal planes to survey the region of

between the processes. Because of the depth and the similar echogenicity of the plexus to

psoas major, however, ultrasound visualization of the nerves may not be possible in older

children. In these patients, instead of real-time guidance the block is usually ultrasound

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aided, meaning that location and depth of the transverse processes are determined using

ultrasound but the actual needle placement is not imaged. In younger children the plexus is

easier to identify because the muscle tissue appears relatively more hypoechoic than the

nerve structures, which contain hyperechoic connective tissue layers (Kirchmair et al., 2004).

It is best to insert the needle in a cephalad or caudad direction rather than medially towards

the spinal canal.


Visualization of the lumbar paravertebral region using sonographic imaging has been described in the literature, with the authors reporting successful intra and postoperative analgesia (Johr, 2005). Although ultrasound may enable visualization of the transverse processes or the plexus itself, use of a nerve stimulator, maintaining a needle puncture relatively lateral and cranial (Schuepfer & Johr, 2005), and performing a regular aspiration during injection are recommended to increase safety of the block. Without clear tracking of the needle tip and it may be difficult to achieve an adequate view of the local anesthetic spread, especially if the needle is inserted in a relatively medial and caudal location (Tsui & Suresh, 2010a). Therefore, a risk-benefit analysis is necessary before performing this block.

There is a lack of data in the pediatric literature describing the use of ultrasound imaging for other blocks of the nerves of the lumbar plexus, notably the fascia iliaca block, 3-in-1 block, or individual blocks of the lateral femoral cutaneous or obturator nerves. However, these blocks could all benefit from the advantages offered by ultrasound guidance. In particular, visualization of local anesthetic spread will likely reduce reliance on injecting larger than necessary volumes of local anesthetic in an attempt to block all of the related nerves (Simion & Suresh, 2007).

2.2.2 Femoral nerve block

2.2.2.1 Sonoanatomy

The femoral nerve originates from nerve roots L2, L3, and L4 and when blocked provides

surgical anesthesia and analgesia for the anterior thigh extending to the knee. The femoral

artery is easily visualized and serves as the principle ultrasound landmark (Figure 6). With

the probe placed perpendicular to the nerve axis (i.e., coronal oblique) at the level of and

parallel to the inguinal crease, the nerve appears lateral to the large, circular, and anechoic

femoral artery. Color Doppler may be helpful to identify the femoral vasculature. The nerve

typically assumes a triangular shape but may be of variable size. The fascia lata (most

superficial) and iliaca (separating the nerve from the artery) are visible superficial to the

femoral nerve and most often appear as bright and longitudinally angled echogenic signals

(Tsui & Suresh, 2010a).

2.2.2.2 Technique

A femoral nerve block may be used for surgical procedures on the anterior thigh and knee,

including anterior thigh biopsy and knee arthroscopy. With the patient supine, the femoral

artery, vein, and nerve can all be visualized with a linear probe placed along the inguinal-

femoral crease. When inserted using an in-plane approach, the needle tip can be visualized

as it enters the fascia iliaca. It is important that the needle be placed inside the fascia iliaca

compartment. In a study comparing ultrasound guidance to nerve stimulator technique, the

nerve was visible in all children studied when the probe was placed parallel and inferior to

the inguinal ligament and lateral to the femoral artery. Ultrasound was also used effectively

to visualize the needle tip and facilitate needle redirections (Oberndorger et al., 2007).

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Fig. 6. Sonoanatomy at the femoral nerve block location using a linear hockey stick probe

(SLA, 6-36 MHz, 25-mm footprint) placed parallel and inferior to the inguinal ligament.


The proximity of the femoral nerve to major vasculature increases the potential for

inadvertent vessel puncture and hematoma formation. Although there is no direct evidence

to prove that ultrasound could reduce this risk, it is the authors’ experience that fewer

adverse events occurred when this block was performed under ultrasound guidance. In

addition, precise ultrasound imaging of the local anesthetic spread may reduce the need for

larger volumes used when injecting blindly.

2.2.3 Sciatic nerve block

2.2.3.1 Sonoanatomy

The sciatic nerve is formed by nerve roots L4 to S3 and innervates the posterior thigh and

leg below the knee, with the exception of the medial portion. As it leaves the pelvis through

the greater sciatic foramen, the sciatic nerve can be found inferior to the gluteus maximus

muscle. The nerve lies between the ischial tuberosity and the greater trochanter, however

typically only the greater trochanter can be seen when using a small foot print linear probe

(Figure 7). Curved probes (curvilinear) with moderate-low frequency (e.g.2-5MHz) allow

deeper ultrasound beam penetration and are often necessary in older children. Although the

greater trochanter and ischial tuberosity serve as the principle bony landmarks for the

subgluteal approach, they must be palpated with great care as these structures do not reach

adult morphology until puberty (Scheuer et al., 2000). Thus, since the size of the greater

trochanter is dependent on the age of the child, it is only highly recognizable at 6 to 8 years

of age (Scheuer, 2000). While the medial aspect of the greater trochanter appears largely

hypoechoic, the sciatic nerve is predominantly hyperechoic and is typically elliptical in a

short-axis view.

The pathway of the sciatic nerve continues through the posterior popliteal fossa before

bifurcating to form the common peroneal and tibial nerves. A linear probe transversely

oriented in the popliteal crease captures both the tibial and common peroneal nerves located

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Fig. 7. Sonoanatomy at the subgluteal location using a linear probe (HFL38, 6-13 MHz,

38mm footprint). Image shows where the sciatic nerve lies at the midpoint between the

ischial tuberosity and the greater trochanter of the femur.

medially and laterally, respectively, to the popliteal vessels (Figure 8). This vasculature,

particularly the popliteal artery, serves as useful ultrasound landmarks (color Doppler may

be useful). At the popliteal crease, the tibial nerve is found more superficial and most

adjacent to the artery. However, as the probe is moved cephalad, the artery becomes deeper

and more distant as the tibial nerve moves laterally to join the common peroneal nerve. At

and cephalad to the bifurcation, the sciatic nerve appears as a large round to flat-oval

hyperechoic structure. The biceps femoris muscle lies superficial to the bifurcating nerves

and appears as a large oval shaped structure with less internal punctuate areas (hyperechoic

spots) than the nerves.

2.2.3.2 Technique

A sciatic block is commonly used for surgical procedures of the foot and ankle, as well as in

combination with a femoral nerve block for patients undergoing knee surgery (De Jose

Maria et al., 2008). In children, subgluteal and popliteal approaches are most commonly

employed. For the subgluteal approach, the child should be in the Sim’s position with the

hip and knee flexed (van Geffen & Gielen, 2006). To visualize the sciatic nerve in cross

section, the probe should be oriented transversely at the mid point of the ischial tuberosity

and the greater trochanter. The nerve can be seen deep to and at the junction where the

gluteus maximus muscle meets the biceps femoris-semitendinosus muscle complex. Both in-

and out-of-plane approaches have been described with success.

For a more distal block of the sciatic nerve at the popliteal fossa, it is best to place the patient

in the prone position with the probe above the popliteal crease. The probe is moved

cephalad until the nerves merge together. Using an in-plane approach, the needle is placed

in close proximity to the sciatic nerve and the local anesthetic spread surrounds the nerve.

To achieve an ideal image, a probe appropriate to the size of the child must be used. Deeper

structures in older children require lower frequency probes for sufficient visualization. Such

a low frequency probe might be necessary for the subgluteal approach as there is

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considerable variation in the depth of the sciatic nerve in older children. In contrast, high-

frequency linear probes are more advantageous for popliteal blocks.

Fig. 8. Sonoanatomy in the popliteal fossa just distal to bifurcation of the sciatic nerve using

a linear hockey stick probe (SLA, 6-13, 25-mm footprint).


Ultrasound imaging can be particularly beneficial when using blind catheter insertion to

confirm the spread of local anesthetic around the nerve. In addition, ultrasound guidance

can be advantageous in instances in which a blind technique is likely to fail. An example of

this was described for patients with venous malformations. The use of ultrasound in these

patients helped the anesthesiologist avoid vascular puncture during needle placement (van

Geffen et al., 2007). Due to the high degree of variability in the division of the sciatic nerve,

ultrasound also offers considerable advantages in nerve localization when using the

popliteal approach (Schwemmer et al., 2004).

2.3 Truncal blocks Truncal blocks are becoming a more popular means of providing analgesia for procedures in

the umbilical or epigastric regions. The ability to visualize relevant musculature and fascial

layers with ultrasound offers an advantage over the more subjective conventional technique of

detecting “pops” or “clicks” upon penetration into fascial compartments. This is particularly

beneficial in children due to the close proximity of nerve and critical abdominal structures. In

addition, visualization of the local anesthetic spread made possible with ultrasonography has

the potential to improve success rates and allow for administration of minimal volumes of

local anesthetic (Willschke et al., 2005, Willschke et al., 2006).

2.3.1 Ilioinguinal-iliohypogastric block

2.3.1.1 Sonoanatomy

The ilioinguinal and iliohypogastric nerves supply the groin area and are derived from the

L1 nerve root of the thoracolumbar plexus. Both nerves are seen as hypoechoic structures

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between the internal oblique and transversus abdominis muscles. A short-axis view of the

ilioinguinal nerve running in the transversus abdominis plane (TAP) can be viewed using a

probe placed medial to the superior aspect of the anterior superior iliac spine (ASIS) (Figure

9). The ASIS appears nodular in shape and hypoechoic due to the dorsal shadowing beyond

the highly reflective periosteum. The lateral abdominal muscles appear with numerous

hyperechoic dots within a hypoechoic background (a “starry night” appearance). Any

hyperechoic divisions between the muscles represent fascial compartments.

Fig. 9. Sonoanatomy of the ilioinguinal-iliohypogastric nerve block location medial to the

ASIS using a linear hockey stick probe (SLA, 6-13 MHz, 25-mm footprint).

2.3.1.2 Technique

This block is commonly used for patients undergoing surgery involving the inguinal region,

including hernia repair, orchiopexy, or groin surgery. When performed successfully, these

blocks can be as effective as caudal blocks and may be used when a caudal block is

contraindicated (Markham et al., 1986). When using a linear probe, it should be placed at the

highest point of the iliac crest with the axis facing the umbilicus. This orientation provides a

clear view of the relevant muscle layers and nerves as they run in the TAP. Using an in-

plane approach, a needle is inserted toward the ilioinguinal and iliohypogastric nerves.

After a small test injection of dextrose (1-2ml) to confirm the spread between the muscles

and close to the nerves, local anesthetic can be injected into the space.


The use of conventional techniques for the ilioinguinal nerve block based on the observance of clicks to determine penetration of the abdominal muscles as a reported success rate of approximately 70% (Lim et al., 2002). Part of the block failure may be attributed to inaccurate nerve localization using traditional landmark-based needle insertion sites and the fascial click method to determine injection. A study by Wientraud et al, used ultrasonography to determine the actual location of local anesthetic distribution when it was

injected using traditional methods. The local anesthetic surrounded the nerves in only 14% of blocks (Wientraud et al, 2008). Thus, the use of ultrasound guidance to visualize the plane of nerve localization, needle trajectory, and local anesthetic dispersion offers significant opportunity for improvement.

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Pharmacodynamic studies have demonstrated the efficacy of lower doses of local

anesthetics for managing postoperative pain in children who received these blocks under

ultrasound guidance. The authors also believe using lower volumes could reduce the risk of

local anesthetic toxicity (Willschke et al., 2006). The use of lower volumes of local anesthetic

is also supported by a recent pharmacokinetic study that found higher plasma levels of

ropivacaine using ultrasound guidance when compared to a single pop technique

(Weintraud et al., 2009).

2.3.2 Transversus Abdominis Plane (TAP) block

2.3.2.1 Sonoanatomy

The TAP is a potential space located between the internal oblique and the transversus

abdominis muscles. The thoracolumbar nerve roots, T8-L1, run in the TAP. The 3 muscle

layers: external oblique, internal oblique, and transversus abdominis, serve as easily

identified landmarks in an ultrasound image (Figure 10). However, there may not be a clear

distinction between the individual muscles. The external oblique is most superficial and lies

above the internal oblique, followed by the transversus abdominis. Deep to the muscles, the

peritoneum appears as a hypoechoic region. The nerves for this block have similar

echogenicity when compared to the muscles and travel tangentially to the ultrasound beam

axis. As a result, the nerves will not be visualized.

Fig. 10. Sonoanatomy at the TAP using a linear hockey stick probe (SLA, 6-13 MHz, 25-mm

footprint).

2.3.2.2 Technique

TAP blocks may be used to provide analgesia for a variety of abdominal procedures as well

as chronic neuropathic abdominal wall pain (McDonnell et al., 2007). This block is

particularly useful when a central neuraxial blockade is contraindicated. Performing a TAP

block in pediatric patients under ultrasound guidance has been described using a step-by-

step approach (Pak et al., 2009). A high-frequency linear probe or hockey stick probe is

placed on the abdomen lateral to the umbilicus. The probe can be shifted laterally to identify

the three layers of the abdominal wall. Next, a needle is placed at or slightly posterior to the

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midaxillary line using an in-plane approach. The needle should be inserted into the plane

between the internal oblique and the transversus abdominis muscles and the local anesthetic

is injected into this potential space. The local anesthetic dispersion will appear as an

elliptical opening of the potential space. If this spread is not observed, it is important to

hydrodissect with small injections of local anesthetic solution or saline until the exact plane

of injection is recognized.


In adults, the anesthesiologist may rely on palpating the lumbar triangle of Petit to find the

internal oblique muscle that lies at its base (Rafi, 2001). However, this triangle is not easily

palpable in children, making ultrasound a valuable tool for determining needle placement.

Because it includes blockade of the first lumbar nerve root, a TAP block may be used instead

of an ilioinguinal/ iliohypogastric block when images from the region anterior and medial to

the ASIS are not ideal (Fredrickson et al., 2008).

3. Neuraxial blocks

Performing central neuraxial blocks in pediatric patients can be challenging, due in part to

the narrow safety margin for needle placement in the spinal canal and tight positioning of

anatomical structures. While the use of ultrasound in neuraxial anesthesia in adults is

somewhat limited because of poor beam penetration through the ossified bony vertebral

column, it could be of much greater value in pediatric patients. In contrast to adults,

children have limited ossification, thus allowing good visual resolution of the anatomy and

block-related equipment or solutions (Tsui & Suresh, 2010b). Despite an increasing amount

of literature supporting the use of ultrasound guided neuraxial blocks, the benefit of

ultrasound has not yet been established for block performance or outcome in all patients.

3.1 Epidural Analgesia 3.1.1 Sonoanatomy Visualization is typically easier in younger children because of the largely cartilaginous composition of their vertebral columns. To capture an overview of neuraxial structures, the probe should be placed both in transverse and longitudinal planes. In a transverse view, the central vertebral body in the region of L3/ L4 appears as a hyperechoic “V” in contrast to the

more hypoechoic paravertebral muscles. Bony structures such as the spinous processes are useful in identifying the midline (Figure 11). The ligamentum flavum and dura mater may be visualized as hyperechoic lines in the transverse view, although the dura mater becomes more difficult to see in children older than 6 months (Tsui & Suresh, 2010b). Deep to the dura, fibers of the cauda equina appear as hyperechoic dots in an anechoic space filled with cerebrospinal fluid. Using a paramedial longitudinal view at the level of the thoracic vertebrae, the spinous processes and laminae are easy to identify as slanted hyperechoic lines. Deep to the ligamentum flavum and dura mater, the spinal cord appears as a hypoechoic structure with two distinguishing features: a central line of hyperechogenicity representing the median sulcus, and a bright outer covering of the pia mater (Figure 12).

3.1.2 Technique A report by Rapp et al. examined the use of ultrasound preoperatively to visualize the sacral,

lumbar, and thoracic regions (Rapp et al., 2005). The authors used ultrasound to measure the

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skin to ligamentum flavum distance to determine the depth of loss of resistance. An assistant

is recommended during catheter placement if real time imaging is desired. In this study a

separate individual positioned the probe in the paramedial longitudinal plane at the level of

insertion while the anesthesiologist performed the epidural puncture. Ultrasound images

were used to monitor the loss of resistance, seen as a ventral displacement of the dura mater

and widening of the epidural space.

Fig. 11. Sonoanatomy of the spinal column and canal in a transverse axis at the L3/ L4 level

using a linear probe (HFL38, 6-13 MHz, 38 mm footprint).

Fig. 12. Sonoanatomy of the spinal column and canal in a paramedian longitudinal view at

the midthoracic level using a linear probe (HFL38, 6-13 MHz, 38 mm footprint).

A randomized controlled trial by Willschke et al. also studied the use of ultrasound

guidance for determining loss of resistance (Willschke et al., 2006). The procedure was

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performed with the child in the lateral position with knees flexed. Similar to the technique

described by Rapp et al, an assistant operated the probe in a paramedial longitudinal plane

while the anesthesiologist performed a midline puncture. The needle was inserted after

visualization of the dura mater and the needle was followed on its course through the

ligamentum flavum into the epidural space. Ultrasound imaging was also used to confirm the

tip of the catheter and local anesthetic spread.

3.1.3 Outcome and discussion Ultrasound imaging for epidural analgesia may be beneficial either preprocedurally (before

puncture) or during (in real time) block performance to estimate the depth to the epidural

space as well as the spread of the local anesthetic. When identifying the epidural space,

studies have found that the dura mater is typically more clearly visible than the ligamentum

flavum (Marhofer et al., 2005; Kil et al., 2007). The benefits of preprocedural ultrasound may

be more substantial in obese children in whom the landmarks are difficult to palpate

(Kawaguchi et al., 2007). A randomized study compared ultrasound guidance with loss of

resistance technique for the placement of both lumbar and thoracic level epidural catheters

(Willschke et al., 2006). Although the authors found ultrasound guidance to be superior in

terms of the number of bone contacts and speed of execution, at this time ultrasound

guidance does not obviate continuous testing for loss of resistance.

There is also evidence to suggest that ultrasound may enable visualization of static

structures like catheters (Chawathe et al., 2003). This is possible by one of two methods:

monitoring the movement of the local anesthetic as the catheter moves through the solution,

or noting the ventral movement of the dura mater.

3.2 Caudal block 3.1.1 Sonoanatomy Preprocedural imaging in both the transverse and longitudinal planes is important to

identify the sacrococcygeal ligament, dural sac, and cauda equina. With the probe placed in

the transverse plane at the level of the coccyx, the sacral hiatus is visible between two

hyperechoic lines: the superior line represents the sacrococcygeal ligament while the inferior

represents the dorsum of the pelvic surface of the sacrum (Figure 13). When the probe is

placed in a longitudinal plane between the sacral cornua, the dorsal surface of the sacrum,

dorsal aspect of the pelvic surface of the sacrum, as well as the sacroccygeal ligament are

viewed. The ligament can be identified as a thick, linear, hyperechoic band that slopes

caudally. When ossification has occurred at the midline, as is the case in older children, the

paramedial longitudinal view is optimal because it allows the ultrasound beam to penetrate

the spaces lateral to the spinous processes (Roberts & Galvez, 2005).

3.2.2 Technique Current research supports the use of ultrasound imaging in both the transverse

(Raghunathan et al., 2008; Schwartz et al., 2008) and longitudinal (Roberts & Galvez, 2005;

Park et al., 2006) planes to guide needle placement during a caudal block. For the transverse

technique, the probe was placed just cephalad to the point of injection. Ultrasound imaging

allowed visualization of local anesthetic injection within the caudal epidural space, made

evident by the presence of localized turbulence and a swelling of the caudal space (Schwartz

et al., 2008).

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Fig. 13. Sonoanatomy of the caudal epidural space at the level of the sacral hiatus using a

linear hockey stick probe (SLA, 6-13 MHz, 25 mm footprint) placed in the transverse plane.

The longitudinal technique allows a long axis view of the needle as is penetrates the

sacrococcygeal ligament and thus is particularly valuable in determining accurate angle and

depth of the needle. Park et al. used ultrasound in children age 2-84 months to determine

the optimal angle of needle entry (Park et al., 2006). The authors found a needle angle of 21

degrees to the skin surface to be successful in 92.3% of patients studied. A similar technique

has been found to be successful for catheter insertion into the caudal space. The position of

the catheter is possible with ultrasound imaging (Roberts & Galvez, 2005).

3.2.3 Outcome and discussion

Caudal blocks for lower extremity and perineal perioperative analgesia are one of the most

commonly practiced regional anesthesia techniques in children. However, they can be

associated with higher rates of complications than peripheral blocks, notably bloody

punctures and intravascular injections (Giaufre et al., 1996; Lacroix, 2008). To reduce these

risks, it is important to have correct needle placement when performing the block. The use

of epidural electrical simulation may be used in conjunction with ultrasound guidance to

ensure proper needle placement within the caudal epidural space. When compared to the

swoosh test for confirming caudal epidural placement, investigators found real time

ultrasonography to have significantly higher sensitivity and negative predictive value

(Raghunathan et al., 2008). The low negative predictive value may be explained in part by

the older age of the patients (5-8 yrs).

Similar to that described in the adult literature, it may be beneficial to use both transverse

and longitudinal planes; the longitudinal plane to view the needle puncture followed by a

transverse plane to ensure local anesthetic dispersion (Chen et al., 2004). Although there is

an increasing amount of literature illustrating the advantages of clearer visualization of

anatomical structures as well as the needle, more evidence is needed to clearly define the

benefits of ultrasound imaging in neuraxial blocks. For the caudal block in particular,

ultrasound guidance may be considered cumbersome for the standard patient, however it

may be a useful tool in obese patients in whom poorly palpable landmarks make the blind

approach more difficult.

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Block Indications Ultrasound Landmark

Axillary Surgery of the elbow, forearm, or hand Axillary artery

Interscalene

Surgery of the shoulder or proximal

arm, catheter placement for

postoperative pain control

Scalene muscles and

subclavian artery

Supraclavicular Most surgical procedures of the upper

extremity distal to the midhumerus Subclavian artery

Infraclavicular

Surgery of the arm and elbow, catheter

placement for major reconstructive

procedures

Subclavian artery and vein

Lumbar plexus Surgery of the hip or knee Transverse processes

Femoral nerve Surgical procedures of the anterior

knee and thigh Femoral artery

Sciatic nerve

Most surgical procedures of the foot

and ankle, may be used in conjunction

with a femoral block for knee surgery

Subgluteal: greater

trochanter and ischial

tuberosity

Popliteal: popliteal artery

Ilioinguinal-

iliohypogastric Hernia repair or groin surgery

Two to three muscle layers

(external oblique and

aponeurosis) and the

anterior superior iliac

spine

Transversus

abdominis plane

Major abdominal procedures, chronic

neuropathic abdominal wall pain

Three muscle layers:

external oblique, internal

oblique, transversus

abdominis

Epidural analgesia

(lumbar)

Surgery of the lower extremity or

abdomen

Ligamentum flavum, dura

mater, and bony structures

(midline spinous processes

in transverse plane,

laminae in paramedial

longitudinal plane)

Caudal Perineal surgery

Dorsum of pelvic surface

of the sacrum and

hyperechoic

sacrococcygeal membranes

on the two coruna

Table 1. Common peripheral and neuraxial nerve blocks in children

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3.3 Spinal anesthesia Although ultrasound imaging has the potential to facilitate needle guidance and

determination of the depth of the subarachnoid space, to the authors’ knowledge there is no

published literature available at this time that has studied this aspect of pediatric spinal

anesthesia.

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Ultrasound ImagingEdited by Mr Masayuki Tanabe

ISBN 978-953-307-239-5Hard cover, 210 pagesPublisher InTechPublished online 11, April, 2011Published in print edition April, 2011

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In this book, we present a dozen state of the art developments for ultrasound imaging, for example, hardwareimplementation, transducer, beamforming, signal processing, measurement of elasticity and diagnosis. Theeditors would like to thank all the chapter authors, who focused on the publication of this book.

How to referenceIn order to correctly reference this scholarly work, feel free to copy and paste the following:

Santhanam Suresh, Lauren J. Taylor and Amar S. Minhas (2011). Ultrasound Imaging for PediatricAnesthesia: A Review, Ultrasound Imaging, Mr Masayuki Tanabe (Ed.), ISBN: 978-953-307-239-5, InTech,Available from: http://www.intechopen.com/books/ultrasound-imaging/ultrasound-imaging-for-pediatric-anesthesia-a-review

pediatric anesthesia: a review - glowm...peripheral nerve blocks 2.1 upper extremity blocks...

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